For many years the problem of disposability has plagued industries, which provide disposable diapers, wet wipes, incontinent garments and feminine care products. While much headway has been made in addressing this problem, one of the weak links has been the inability to create an economical coherent fibrous web, which will readily dissolve or disintegrate in water, but still have in-use strength. See, for example, U.K. patent disclosure 2,241,373 and U.S. Pat. No. 4,186,233. Without such a product, the ability of the user to dispose of the product by flushing it down the toilet is greatly reduced, if not eliminated. Furthermore, the ability of the product to disintegrate in a landfill is quite limited because a large portion of the product components, which may well be biodegradable or photode-gradable, are encapsulated in or bound together by plastic which degrades over a long period of time, if at all. Accordingly, if the plastic disintegrated in the presence of water, the internal components could degrade as a result of the rupture of the plastic encapsulation or binding.
Disposable diapers, feminine care products and adult incontinent care products usually comprise a body side liner which must rapidly pass fluids, such as urine or menses, so that the fluid may be absorbed by an absorbent core of the product. Typically, the body side liner is a coherent fibrous web, which desirably possesses a number of characteristics such as softness and flexibility. The fibrous web of the body side liner material is typically formed by wet or dry (air) laying a generally random plurality of fibers and joining them together to form a coherent web with a binder. Past binders have preformed this function well. From an environmental standpoint, it might be stated that the past binders have performed this function too well in that the binders tended not to degrade and thus the liner remained intact, severely hampering any environmental degradation of the disposable product.
Recent binder compositions have been developed which are more environmentally responsible and exhibit better water solubility than past binders. One class of binders includes polymeric materials having inverse solubility in water. These binders are insoluble in warm water, but are soluble in cold water, such as found in a toilet. It is well known that a number of polymers exhibit cloud points or inverse solubility properties in aqueous media. These polymers have been cited in several publications for various applications, including (1) as evaporation retarders (JP 6207162); (2) as temperature sensitive compositions, which are useful as temperature indicators due to a sharp color change associated with a corresponding temperature change (JP 6192527); (3) as heat sensitive materials that are opaque at a specific temperature and become transparent when cooled to below the specific temperature (JP 51003248 and JP 81035703); (4) as wound dressings with good absorbing characteristics and easy removal (JP 6233809); and (5) as materials in flushable personal care products (U.S. Pat. No. 5,509,913, issued to Richard S. Yeo on Apr. 23, 1996 and assigned to Kimberly-Clark Corporation).
Other recent binders of interest include a class of binders, which are ion-sensitive. Several U.S. and European patents assigned to Lion Corporation of Tokyo, Japan, disclose ion-sensitive polymers comprising acrylic acid and alkyl or aryl acrylates. See U.S. Pat. Nos. 5,312,883; 5,317,063; and 5,384,189; as well as, European Patent No. 608460A1. In U.S. Pat. No. 5,312,883, terpolymers are disclosed as suitable binders for flushable nonwoven webs. The disclosed acrylic acid-based terpolymers, which comprise partially neutralized acrylic acid, butyl acrylate and 2-ethylhexyl acrylate, are suitable binders for use in flushable nonwoven webs in some parts of the world. However, because of the presence of a small amount of sodium acrylate in the partially neutralized terpolymer, these binders fail to disperse in water containing more than about 15 ppm Ca2+ and/or Mg2+. When placed in water containing more than about 15 ppm Ca2+ and/or Mg2+ ions, nonwoven webs using the above-described binders maintain a tensile strength greater than 30 g/in, which negatively affects the “dispersibility” of the web. The proposed mechanism for the failure is that each calcium ion binds with two carboxylate groups either intramolecularly or intermolecularly. Intramolecular association causes the polymer chain to coil up, which eventually leads to polymer precipitation. Intermolecular association yields crosslinking. Whether intramolecular or intermolecular associations are taking place, the terpolymer is not soluble in water containing more than about 15 ppm Ca2+ and/or Mg2+. Due to the strong interaction between calcium ions and the carboxylate groups of the terpolymer, dissociation of the complex is highly unlikely because this association is irreversible. Therefore, the above-described polymer that has been exposed to a high Ca2+ and/or Mg2+ concentration solution for about 8 hours or more will not disperse in water even if the calcium concentration decreases. This limits the application of the polymer as a flushable binder material because most areas across the U.S. have hard water, which contains more than 15 ppm Ca2+ and/or Mg2+.
Although many patents disclose various ion and temperature sensitive compositions for flushable materials, there exists a need for flushable products possessing softness, three dimensionality, and resiliency; wicking and structural integrity in the presence of body fluids at body temperature; and true fiber dispersion after toilet flushing so that fibers do not become entangled with tree roots or at bends in sewer pipes. Moreover, there is a need in the art for flushable products having water-dispersibility in all areas of the world, including soft and hard water areas. Such a product is needed at a reasonable cost without compromising product safety and environmental concerns, something that past products have failed to do.